Trace messages are used in electronic data communication installations to provide end-to-end connectivity check. A typical trace message is a repeating message. Each instance of the message is divided in fragments and distributed over a series of data frames. Under the SONET standard, a trace message has 64 bytes, and each data frame carries 1 byte of the message. Hence, an instance of the trace message is distributed over 64 frames. A trace message byte can be carried in the J1 byte slot to provide a path layer connectivity check. The J0 byte slot is reserved for trace message bytes that provide end-to-end connectivity check at the section layer. Although not currently implemented, trace messages can also be used to provide end-to-end connectivity check at the line layer.
Under the SDH standard, a typical trace message has 16 bytes.
Trace messages propagating in a communication link are subjected to very basic processing techniques when they are received by an intermediate device on the communication link or by a terminal device. In the case of an intermediate device, the trace message is simply retransmitted. In the case of a terminal device, a check is performed to determine if anomalies are present in the received instance of the message. In the affirmative, an alarm is triggered.
Sometimes, anomalies in a trace message can occur as a result of overhead slips in a Transparent Multiplexing (TMUX) connection caused by frequency offsets between processing equipment and the TMUX connection. Such overhead slips induce spurious anomalies in one or more trace message instances that can trigger false alarms in the terminal device.
Against this background, there appears the need in the industry to provide more sophisticated techniques to process trace messages in a communication network.